1. Field of the Invention
The present invention is concerned with improved fiber-reinforced dental porcelain compositions which can be used to good effect in the fabrication of dental restorations such as inlays, onlays, crowns and pontics. More particularly, it is concerned with such reinforced dental porcelains characterized by the presence of relatively minor amounts of zirconium oxide ceramic fibers therein.
2. Description of the Prior Art
Various porcelain ceramics have been used in the past in restorative dentistry, inasmuch as these materials can be used to produce aesthetically pleasing restorations which closely mimic the look and feel of natural teeth. Most dental porcelains are felspar-based, and contain a substantial fraction of silicon dioxide, typically on the order of 50% or more. Apart from SiO.sub.2 dental porcelains, porcelains also typically include balancing oxides, fluxes, modifiers and an intermediate, commonly aluminous oxide, Al.sub.2 O.sub.3. The stability of finished ceramic restorations made from dental porcelains is highly dependent upon the silicon-oxygen lattice developed in the dental glass. As a consequence, covalent bonding within the glass structure must not be reduced significantly, else problems of hydrolytic stability and devitrification may arise.
A persistent problem encountered in connection with dental porcelains is the tendency of the resultant dental restorations to be relatively brittle and subject to breakage. Indeed, this tendency is the prime drawback of all-porcelain restorations. Attempts have been made in the past to strengthen dental porcelain by the inclusion of crystalline oxide powders such as quartz and alumina. Moreover, it has been suggested in the past to employ relatively large quantities of silica-alumina-zirconia refractory glass fibers as an additive in dental porcelains. Thus, U.S. Pat. No. 3,069,773 to Saffir discloses the concept of supplementing dental porcelains with from about 5 to 67% of highly refractory glass fibers including substantial quantities of silica and aluminum, and minor proportions of zirconia. A problem with this approach, however, stems from the fact that such relatively large quantities of reinforcing fiber may tend to reduce the extent of covalent bonding in the silicon-oxygen lattice of the porcelain.
It has further been suggested to employ silicon carbide fibers for the reinforcement of porcelain crowns, Derand, "Reinforcement of Porcelain Crowns with Silicon Carbide Fibers", J. Pros. Dent. (January 1980). This technique is of very limited utility, however, inasmuch as the silicon carbide fibers are very dark in color and therefore can be used only in a very small core portion of the restoration, else the aesthetic aspects of the restoration are unacceptable.
In short therefore, the problem of strengthening dental porcelains, while long recognized and the subject of prior research, has remained a troublesome problem which has heretofore not been satisfactorily resolved.